Autosampler syringe with compression sealing

ABSTRACT

A fluid transfer device includes a cylinder and a displacement rod. The cylinder is fabricated rigid enough to minimize distortion of volume yet compliant enough to create a seal between itself and the surface of the displacement rod. The cylinder is constructed with a bore hole through its central portion running from end to end. The diameter of the bore hole is larger than the diameter of the displacement rod. The displacement rod is constructed of a rigid material. At least one end of the cylinder has a diameter reduced so the diameter of the bore hole and the diameter of the displacement rod are substantially the same to form a seal with each other. As the displacement rod is withdrawn from the bore hole, a sample is drawn into the bore hole. The volume of the sample drawn into the bore hole is a function of the volume of the displacement rod withdrawn from the bore hole. A cross hole, for venting undesired fluid such as gas bubbles or previous sample(s), is located on the displacement rod. The cross hole is connected to a passageway through the inside of the displacement rod leading to an opening on its surface which is outside of the cylinder.

FIELD OF THE INVENTION

[0001] The present invention relates to liquid chromatography apparatus,and more particularly to a syringe used by an autosampler to acquiresamples of liquids.

BACKGROUND OF THE INVENTION

[0002] In various analytical procedures, including liquidchromatography, a large number of liquid samples are processedsequentially in the same apparatus. An autosampler is used to obtainsamples of liquids which are to be analyzed. The autosampler typicallyuses a syringe to acquire the sample. Performance of autosamplers issignificantly influenced by the accuracy of sample acquisition and wearresistance of the syringe. Various configurations of syringes used toobtain liquid samples are known in the art.

[0003] An example of one type of known syringe is generally illustratedin FIG. 1. This prior syringe comprises a cylinder 10, having a firstand a second end. The cylinder 10 is typically made of glass. Thecylinder 10 has a bore hole 12 through its central portion which extendsfrom the first end to the second end. A piston 14 which enters the borehole 12 through the first end of the cylinder 10, is configured to slidein and out of the bore hole 12. A plunger 16 is attached to the piston14 at an end portion thereof and is configured to be inserted forslidable engagement in the bore hole 12. The plunger 16 is typicallymade of Teflon. The area where the plunger 16 and the bore hole 12 comeinto contact creates a liquid tight seal. As the piston 14 is pulled outof the bore hole 12, the plunger 16 creates a vacuum which draws asample into the bore hole. This necessitates that the bore hole 12 andthe plunger 16 be fabricated within strict tolerances to achieve desiredaccuracy of sample.

[0004] A metal coupling 20 is disposed at the second end of the cylinder10. A portion of the metal coupling 20 is threaded for attachment tomechanisms for initially receiving the acquired sample e.g., hose,needle (not shown). The metal coupling 20 has a Teflon seal 22 whichserves to seal the connection between the glass 10 and the receivingmechanisms.

[0005] During the initial operation or process of collecting samples,undesired fluid such as gas bubbles or prior liquids may collect insidethe bore hole 12. The presence of undesired fluid in the bore hole 12can, among other things, adversely influence the accuracy of delivery ofthe syringe. In prior art syringes, it is a difficult task to remove theentrapped undesired fluid. To purge undesired fluid from the bore hole12 the piston 14 and plunger 16 must be manually removed from the borehole 12. Fluid may spill out and compromise the integrity andcleanliness of the fluid delivery system. Furthermore, removal ofundesired fluid such as gas bubbles, typically cannot be done in anautomated mode.

[0006] Additionally, in the prior art syringe illustrated in FIG. 1, theaccuracy of the bore hole 12 is poor as its precision is limited by manyfactors in the manufacturing process. Present practice is to heat shrinka glass tube onto a wire mandrel. The wire mandrel diameter changes asit wears during extraction from the glass tube after cooling. Thecoefficients of thermal expansion vary from lot to lot and according totemperature variations so that producing a wire mandrel to a precisiondiameter is difficult. All of these factors result in an influence orpotential variability of 1.22% in volume for a 250 microliter syringe.It would be very costly to reduce this influence because it would causea high rejection rate to the vendor.

[0007] Another problem associated with the illustrated prior art syringeis that the plunger 16 on the piston 14 is influenced by friction withthe bore hole 12. This friction can distort the plunger 16 by varyingamounts dependent upon the coefficient of friction of the bore hole. Anengineering estimate from finite element analysis indicatesapproximately 0.5% variability due to friction at 1 microliterinjections. Still further, the Teflon seal 22 at the coupling 20 expandsas the temperature rises, and because it is confined it has a tendencyto yield. As the temperature of the Teflon seal 22 drops, the sealcontracts, sealing pressure of the seal drops and the seal will leak.Also, if there is a long time period between draws to fill the syringe,the bore dries out and can influence precision by varying friction.Variability of friction can lead to premature wear.

[0008] Another prior art syringe is disclosed in U.S. Pat. No. 4,625,572(the '572 patent). The '572 patent provides a cylinder pump for anautomatic chemical analyzer or the like, which comprises a cylinder anda plunger. Both the cylinder and plunger are made of a rigid material.They are coupled together in a liquid tight sliding contact with eachother without any elastic member such as an o-ring interposed betweenthe sliding contact surfaces. Because the plunger and cylinder must becoupled together in a liquid tight sliding contact, both must bemachined within strict tolerances. Machining the plunger and cylinderwithin strict tolerances is an expensive process.

[0009] The '572 patent discloses the use of substantially the samematerial for both the cylinder and the plunger to maintain stricttolerances. This limits the effectiveness of the cylinder pump bynecessitating the use of materials which are acceptable for both aplunger and a cylinder and may not be transparent. A compromise resultsin that materials can not be used which are ideally suited for userespectively as a plunger or a cylinder. The '572 patent also requiresthat the contact surfaces of both the cylinder and the plunger bepolished to a mirror-like finish. This further complicates manufacturingand increases the cost of the cylinder pump.

[0010] Furthermore, the '572 patent provides no mechanism for removal ofundesired fluid from the bore hole. Undesired fluid trapped in the borehole can significantly reduce the accuracy of pumped volumes, andnegatively affects the efficiency of the subsequent analysis of samples.

SUMMARY OF THE INVENTION

[0011] The present invention provides a fluid transfer apparatus havingintegrated end sealing which is inexpensive to manufacture, highlyaccurate and lasts significantly longer than previous fluid transferdevices.

[0012] According to the invention a fluid transfer device is providedfor use in an autosampler. The fluid transfer device comprises acylinder having integrated end seals sealing a displacement rod. Thecylinder according to the invention is fabricated of a material such asUltra High Molecular Weight (UHMW) plastic or the like which is rigidenough to minimize distortion of volume yet compliant enough to create aseal between itself and the surface of the displacement rod. Thecylinder, has a first sealing end and a second sealing end, and isconstructed as an integrated structure with a bore hole through itscentral portion, running from end to end. The diameter of the bore holeis larger than the diameter of the displacement rod. The bore holeaccording to the invention does not need to be machined to any specialtolerances. The displacement rod is constructed of a rigid material andis dimensioned as a function of the volume of fluid that is desired tobe displaced through the syringe. At the first end of the cylinder thediameter of the cavity decreases until the diameter of the cavity andthe diameter of the displacement rod are substantially the same so as toform a compression seal between the rod and syringe.

[0013] The second end of the cylinder has an integrated externallythreaded coupling configured to be attached to mechanisms for receivingthe acquired sample, such as a needle or hose(s). As the displacementrod is withdrawn from the bore hole, a sample is drawn into the fluidtransfer device. The volume of the sample drawn into the bore hole willbe substantially the same as the volume of the displacement rodwithdrawn from the bore hole. Additionally, a cross hole, for ventinggas bubbles or other undesirable fluids (e.g. left over previousliquid(s)), is located on the displacement rod at a point so that it maybe positioned inside the bore hole. The cross hole is connected to apassageway through the inside of the displacement rod leading to anopening on the surface of the displacement rod which, when the rod is inan appropriate position, leads outside of the cylinder. Thus undesiredfluid inside the bore hole can be vented when the cross hole isappropriately positioned within the bore and a flow is induced by aslight positive pressure.

[0014] In an alternative embodiment according to the invention, adifferential displacement configuration is provided wherein the innerdiameters of seals disposed at extreme ends of a cylinder have differentdimensions, to accommodate a displacement rod having different outerdiameter dimensions. The displacement rod has two different outerdiameters to allow very low volume samples to be drawn without requiringan unmanageably small diameter displacement rod.

[0015] Features of the invention include provision of a syringe havingincreased accuracy, lower cost and increased longevity. The entirecylinder portion can be fabricated as a unitary structure havingexternal compression sealing which simplifies the manufacturing process,provides enhanced sealing and saves money. The syringe is configuredwith a bore hole inner diameter that is not critical thus saving thesubstantial cost and avoiding the complexities of manufacturingassociated with maintaining precise tolerances. The seal created by thedisplacement rod and the cylinder wears more slowly than prior seals andis effectively retained by compressive forces exerted continuously onthe exterior of the seal area. This results in a significant improvementin seal longevity over prior fluid transfer devices. In addition, thepresent invention allows the use of an automatic gas purge. By allowingfor the automatic release of undesired fluid from the bore hole thepresent invention further increases accuracy over prior devices.

BRIEF DESCRIPTION OF THE DRAWING

[0016] The foregoing and other features and advantages of the presentinvention will be more fully understood from the following detaileddescription of illustrative embodiments, taken in conjunction with theaccompanying drawing in which:

[0017]FIG. 1 is an illustration of a prior art autosampler syringe;

[0018]FIG. 2 is an illustration of an autosampler syringe according topresent invention;

[0019]FIG. 3 is an illustration of an alternative embodiment of anautosampler syringe according to the present invention;

[0020]FIG. 4 is an illustration of another alternative embodiment of anautosampler syringe according to the present invention configured as adifferential displacement syringe; and

[0021]FIG. 5 is an illustration of still another alternative embodimentof an autosampler syringe according to the present invention.

DETAILED DESCRIPTION

[0022] An autosampler syringe of the present invention is generallyillustrated in FIG. 2. In this illustrative embodiment, a syringe isshown comprising a cylinder 30, having unitary, integral first end 31and second end 33, and a displacement rod 32. The cylinder 30 has a borehole 34 through its central portion which extends from the first end 31to the second end 33. In the present invention no critical boretolerance is required, as bore sealing is not a function of the internalbore diameter, thus significantly lowering cost of manufacturing thepresently disclosed syringe. A constant area seal 36 is located at thefirst end 31 of the cylinder 30. In this illustrative embodiment, theconstant area seal 36 and the cylinder 30 are manufactured as a unitarystructure further reducing manufacturing costs. The displacement rod 32is slidably inserted in the bore hole 34 through a hole in the constantarea seal 36. The outside diameter of the displacement rod isdimensioned to tightly yet slidably contact the constant area seal 36 toform a substantially liquid tight seal. Accordingly, there is no wearbetween the displacement rod 32 and the inner walls of the bore hole 34because they do not come into contact with each other. The cylinder inthis illustrative embodiment is unitarily produced using Ultra HighMolecular Weight Plastic.

[0023] A fitting portion 38 of the displacement rod 32 remains outsideof the cylinder 30 and has a fitting either mechanically fastened to orunitarily integrated with the displacement rod 32. The fitting 38 isconfigured to be connected to a mechanical actuator as a function of theinstrument in which the autosampler syringe is to be installed. Themechanical actuator, as known in the art, moves the displacement rod 32in or out of the bore hole 34 to acquire or expel a sample. Thedisplacement rod 32 has a crosshole 40 at a point where it can either bepositioned inside the bore hole 34 or outside of the constant area seal36. When the cross hole 40 is positioned outside the constant area seal36 it has no effect on the drawing in or discharge of a sample. When thecross hole 40 is positioned inside the bore hole 34, it allows undesiredfluid trapped inside the bore hole 34 to be vented. Undesired fluid isvented to outside the bore hole 34 through a pathway inside thedisplacement rod 32 to the end of the displacement rod 32 and through avent hole 42. The fitting portion 38 has a ridged end 44 or other meansof connection so that a flexible hose or other conduit can be attachedfor the purpose of diverting undesired fluid to a waste containment area(not shown).

[0024] The second end 33 of the cylinder 30 is formed into a threadedprotrusion 46 for attachment to known mechanisms for receiving theacquired sample (not shown). The threaded protrusion 46 in thisillustrative embodiment also acts as a static seal between the cylinder30 and the receiving mechanisms. The static seal will not lose itsintegrity upon undergoing heating and cooling as does the Teflon sealused by many prior art fluid transfer devices as it is unitary andintegral to the cylinder and does not involve engagement of materialshaving significantly dissimilar coefficients of thermal expansion.

[0025] In an alternative embodiment, referring still to FIG. 2, a splitring c-shaped clamp 48 is placed around the constant area seal 36 tofurther increase the efficacy and longevity of the seal. The split ringc-shaped clamp 48 serves to exert a force on the constant area seal 36and in the event of any wear between the constant area seal 36 and thedisplacement rod 32, the split ring c-shaped clamp 48 exerts continuousexternal forces on the constant area seal to maintain sealing engagementbetween the seal 36 and the displacement rod 32. This configurationmaximizes the length of time that the seal is maintained beforereplacement is necessary.

[0026] Another alternative embodiment of this invention is illustratedin FIG. 3. A cylinder 30′ and seal 36′ are provided as a non-unitarystructure. The cylinder 30′ is constructed of a material which willprovide high rigidity such as a metal like stainless steel or a plasticsuch as polyetheretherketone (PEEK). The constant area seal 36′ isconstructed of Teflon or another material with a substantially lowcoefficient of friction. In this embodiment the constant area seal 36′is seated in abutment against a surface 35 of the cylinder 30′. The seal36′ is attached to the first end of the cylinder 30′ with a Bellevillewasher 50′.

[0027] A split ring c-shaped clamp 48′ can be placed around the constantarea seal 36′ to provide continuous external forces and further increasethe efficacy and longevity of the seal 36′. The split ring c-shapedclamp 48′ serves to exert a force on the constant area seal 36′ so thatin the event of any wear between the constant area seal 36′ and thedisplacement rod 32′, the split ring c-shaped clamp 48′ ensures that theseal will be maintained.

[0028] Still another alternative embodiment is illustrated in FIG. 4. Adifferential displacement configuration is shown, according to theinvention, comprising a cylinder 68, having a first end 54 and a secondend 56 and a displacement rod 64. The cylinder 68 has a bore hole 58through its central portion which extends from the first end 54 to thesecond end 56. In this alternative embodiment, as in the aforementionedembodiments, no critical bore tolerance is required, as sample volume isnot a function of the internal bore diameter. The cylinder 52 has afirst constant area seal 60 located at the first end 54 and a secondconstant area seal 62 located at the second end 56.

[0029] The displacement rod 64, having a larger diameter portion 66 anda smaller diameter portion 68 is slidably inserted through an opening inthe first constant area seal 60 and through an opening in the secondconstant area seal 62, so that part of the larger portion 66 of thedisplacement rod 64 and part of the smaller portion 68 of thedisplacement rod 64 fits inside the cylinder 52. The larger diameterportion 66 and the smaller diameter portion 68 of the displacement rod64 create a fluid tight seal with the inside sealing surfaces of thefirst constant area seal 60 and the second constant area seal 62,respectively.

[0030] A fluidic connection 70 is located on the cylinder 52. Thefluidic connection 70 is configured to be connected to a mechanism forreceiving an acquired sample. When the larger diameter portion 66 of thedisplacement rod 64 is slid out of the cylinder 52 a sample is drawninto the bore hole 58 through the fluidic connection 70. The sampledrawn is a function of the difference in diameter between the largerdiameter portion 66 and the smaller portion 68 of the displacement rod64 and the magnitude to which the displacement rod 64 is drawn from thecylinder 52. This allows very low volume samples to be drawn withoutrequiring an unmanageably small diameter displacement rod.

[0031] Additionally, a first and second split ring c-shaped clamp 72, 74can be placed around the first and second constant area seal 60, 62,respectively, to provide continuous external forces and further increasethe efficacy and longevity of the seal 60, 62. The first split ringc-shaped clamp 72 serves to exert a force on the first constant areaseal 60 so that in the event of any wear between the first constant areaseal 60 and the larger portion 66 of the displacement rod 64, the firstsplit ring c-shaped clamp 72 ensures that the seal 60 will bemaintained. The second split ring c-shaped clamp 74 serves to exert aforce on the second constant area seal 62 so that in the event of anywear between the second constant area seal 62 and the smaller portion 68of the displacement rod 64, the second split ring c-shaped clamp 74ensures that the seal 62 will be maintained. The purge capabilityincluding the cross-hole illustrated in FIG. 2 and FIG. 3 (although notshown in FIG. 4) can also be implemented.

[0032] Although the device described herein above is shown withreference to its use in an autosampler, it may be used in otherapplications to transfer fluid.

[0033] Although the illustrative embodiment described herein includes acylinder made of Ultra High Molecular Weight plastic, one skilled in theart would appreciate that other materials that are rigid but create aseal with the displacement rod may be used such as PEEK or other inertmaterial.

[0034] Although, one embodiment described herein includes a Bellevillewasher to attach the constant area seal to the cylinder, one skilled inthe art would appreciate that the constant area seal could be attachedby other means such as heat bonding the cylinder to hold the constantarea seal, including an end cap such as illustrated in FIG. 5, latches,hardware, mating threads or the like.

[0035] While the device described herein includes one or two seals, oneskilled in the art would appreciate that still more seals may used as afunction of the application.

[0036] Although the illustrative embodiment described herein includes a“cylinder” with a displacement rod disposed therein receiving thesample, it should be appreciated that other containers having geometricproportions other than cylindrical can be implemented. For instance acontainer having rectangular, hexagonal, triangular, pentagonal crosssections, or the like, could be implemented wherein the volume of sampledisplaced is a function of the dimensions of the displacement rod.Furthermore, it will be appreciated that the cross section of thedisplacement rod may be cylindrical, rectangular, hexagonal, triangular,pentagonal, or the like.

[0037] Although the invention has been shown and described with respectto exemplary embodiments thereof, various other changes, omissions andadditions in the form and detail thereof may be made therein withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A fluid transfer apparatus comprising: acontainer having a first end and a second end and being made of asubstantially rigid material, said container having a substantiallyhollow bore extending therethrough from said first end to said secondend; a constant area seal located at said first end, said constant areaseal having an inside sealing surface and an exterior surface; adisplacement rod slidably inserted through an opening in said constantarea seal so that a portion of said displacement rod fits inside saidcontainer, said displacement rod contacting said inside sealing surfaceof said constant area seal while being slid in an out of said containerthrough said constant area seal while a substantially fluid tight sealis maintained between said constant area seal and said displacement rod;whereby a fluid sample is acquired in said substantially hollow bore asa function of the dimensions of said displacement rod and motion of saiddisplacement rod in said hollow bore.
 2. The fluid transfer apparatus ofclaim 1 wherein at least one of said constant area seal and saidcontainer is made of a material selected from a group consisting ofTeflon, stainless steel, UHMW and PEEK.
 3. The fluid transfer apparatusof claim 1 wherein said displacement rod further includes a cross holeand a passageway, said passageway being positionable within saidcontainer to vent an undesired fluid through said passageway to outsideof said container.
 4. The fluid transfer apparatus of claim 1 wherein aninterior surface of said constant area seal is substantiallycompressible and said exterior surface is configured to receive a clampto continuously constrict said constant area seal to seal said interiorsurface against said displacement rod.
 5. The fluid transfer apparatusof claim 4 wherein said clamp is a split ring c-shaped clamp.
 6. Thefluid transfer apparatus of claim 1 wherein said container and saidconstant area seal are formed as a unitary structure constructed of asubstantially rigid material.
 7. The fluid transfer apparatus of claim 6wherein said unitary structure is made of a material selected from atleast one of UHMW and PEEK.
 8. The fluid transfer apparatus of claim 6wherein an interior surface and said exterior surface of said constantarea seal are substantially compressible and a clamp is secured aroundsaid exterior surface to continuously constrict said constant area seal.9. The fluid transfer apparatus of claim 8 wherein said clamp is a splitring c-shaped clamp.
 10. The fluid transfer apparatus of claim 1 ,wherein said second end of said container comprises a static sealconfigured to be connected to mechanisms for receiving an acquiredsample.
 11. The fluid transfer apparatus of claim 1 , wherein saidsecond end of said container comprises a second constant area sealhaving a second inside sealing surface and wherein said displacement rodhas a first outer diameter configured to slidably engage said constantarea seal and a second outer diameter configured to slidably engage saidsecond constant area seal.
 12. A fluid transfer apparatus comprising: acontainer having a first end and a second end and being made of asubstantially rigid material, said container having a substantiallyhollow bore extending therethrough from said first end to said secondend; a first seal located at said first end; a second seal located atsaid second end; a displacement rod sidably inserted through an openingin one of said first and second seal so that a portion of saiddisplacement rod fits inside said container, said displacement rodfurther including a cross hole and a passageway, said cross hole beingpositionable within said container to vent an undesired fluid throughsaid passageway to outside of said container.
 13. The fluid transferapparatus of claim 12 wherein said second seal is a constant area sealhaving an inside sealing surface and an exterior surface.
 14. The fluidtransfer apparatus of claim 13 wherein said displacement rod contactssaid inside sealing surface of said constant area seal while being slidin an out of said container through said constant area seal and asubstantially fluid tight seal is maintained between said constant areaseal and said displacement rod.
 15. The fluid transfer apparatus ofclaim 12 wherein a fluid sample is acquired in said substantially hollowbore as a function of dimensions of said displacement rod and motion ofsaid displacement rod in said substantially hollow bore.
 16. A fluidtransfer apparatus comprising: a container having a first end and asecond end and being made of a substantially rigid material, saidcontainer having a substantially hollow bore extending therethrough fromsaid first end to said second end; a fluidic connection located on saidcontainer, said fluidic connection configured to be connected to atleast one mechanism for receiving an acquired sample whereby a sampleflows between said substantially hollow bore and said at least onemechanism for receiving an acquired sample; a first constant area seallocated at said first end, said first constant area seal having a firstinside sealing surface and a first exterior surface; a second constantarea seal located at said second end, said second constant area sealhaving a second inside sealing surface and a second exterior surface,said second inside sealing surface being substantially smaller indiameter than said first inside sealing surface; a displacement rod,having a large diameter portion and a small diameter portion, slidablyinserted through an opening in said first constant area seal and throughan opening in said second constant area seal, a portion of said largediameter portion and a portion of said small portion fitting inside saidcontainer, said large diameter portion contacting said first insidesealing surface of said first constant area seal and said small diameterportion contacting said second inside sealing surface of said secondconstant area seal while said displacement rod is slid in and out ofsaid container and a substantially fluid tight seal is maintainedbetween said first and second constant area seals and said large andsmall portions of said displacement rod, respectively; whereby a fluidsample is acquired in said substantially hollow bore as a function ofdifference in dimensions of said large and small portions of saiddisplacement rod and as a function of motion of said displacement rod insaid substantially hollow bore.
 17. The fluid transfer apparatus ofclaim 16 wherein at least one of said first constant area seal, saidcontainer and second constant area seal is made of a material selectedfrom a group consisting of Teflon, UHMW, stainless steel and PEEK. 18.The fluid transfer apparatus of claim 16 wherein said exterior surfaceof at least one of said first and second constant area seal issubstantially compressible and is configured to receive a clamp tocontinuously constrict said at least one of said first and secondconstant area seal.
 19. The fluid transfer apparatus of claim 18 whereinsaid clamp is a split ring c-shaped clamp.
 20. The fluid transferapparatus of claim 16 wherein said container, said first constant areaseal, and said second constant area seal are formed as a unitarystructure constructed of a substantially rigid material.
 21. The fluidtransfer apparatus of claim 16 wherein said displacement rod furtherincludes a cross hole and a passageway, said passageway beingpositionable within said container to vent an undesired fluid throughsaid passageway to outside of said container.